1. Technical Field
The present invention relates to an imaging device and a signal correcting method.
2. Related Art
Recently, as the resolution of a solid-state imaging element such as a charge coupled device (CCD) image sensor and a complementary metal oxide semiconductor (CMOS) image sensor becomes higher, a demand for an information equipment having an imaging function such as a digital still camera, a digital video camera, a cellular phone, and a personal digital assistant (PDA) is rapidly increasing. In the meantime, the information device having an imaging function as described above is referred to as an imaging device.
However, a focus control method which adjusts a focus on a main subject by detecting a distance to a major subject includes a contrast auto focus (AF) method and a phase difference AF method. Since the phase difference AF method may detect a focusing position with high precision at a high speed as compared with the contrast AF method, the phase difference AF method is widely employed in various imaging devices.
As a solid-state imaging element which is mounted in an imaging device which controls a focus by a phase difference AF method, a solid-state imaging element in which a pair of focus detecting pixel cells having openings of a light shielding layer, which are off-centered in reverse directions to each other, are discretely provided on an entire surface of an imaging region is used (see Patent Literature 1 (JP-A-2010-62640)).
An area of the opening of the light shielding layer of the focus detecting pixel cell is smaller than those of other normal pixel cells, and as a result, it is insufficient to use the output signal as an imaging signal. Therefore, it is required to correct the output signal of the focus detecting pixel cell.
Patent Literature 1 discloses a method that selectively performs interpolation correction processing which interpolates and creates an output signal of a focus detecting pixel cell using an output signal of a normal pixel cell therearound and gain correction processing which corrects the output signal of the focus detecting pixel cell by amplifying a gain in accordance with variation of the output signal of the normal pixel cell around the focus detecting pixel cell.
In the imaging device disclosed in Patent Literature 1, when there is a strong light source within or near an imaging range, ghost or flare may be undesirably generated by the reflection on a surface of a lens which configures the optical system or a surface of a chip of a solid-state imaging element. When the light which generates the ghost or the flare is incident onto a focus detecting pixel cell, a defocus amount may not be calculated with high precision, that is, the focus may not be controlled.
A technology which prevents the phase difference AF precision from being deteriorated due to light which generates the ghost or flare is disclosed in Patent Literature 2 (JP-A-2008-242333) and Patent Literature 3 (JP-A-2006-184321).
Patent Literature 2 discloses a method which determines whether the ghost or flare is generated and corrects an output signal of the focus detecting pixel cell when it is determined that the ghost or flare is generated to improve the phase difference AF precision.
Patent Literature 3 discloses a method which detects a position and light amount of a photographing light source from an output of a solid-state imaging element and calculates a correction value from information on the position and the light amount of the photographing light source and information on light which generates a ghost or a flare in accordance with a position of a photographing light source which has been stored in a storing unit in advance to correct a light amount distribution for an image of a subject output from the solid-state imaging element using the correction value, thereby improving the phase difference AF precision.